1. Field
Apparatuses and methods consistent with exemplary embodiments relate to bulb-type semiconductor light-emitting device lamps having wide light distribution characteristics.
2. Description of the Related Art
A light-emitting diode (LED) is a semiconductor light-emitting device that converts electrical signals into light by using, for example, a compound semiconductor. A semiconductor light-emitting device, such as an LED, has a longer lifespan, uses a lower voltage, and requires lower consumption power than other existing light-emitting devices. Also, the semiconductor light-emitting device has excellent response speed and impact-resistant characteristics and can be manufactured to be small and lightweight. The semiconductor light-emitting device may generate different wavelengths of light according to the type and composition of a semiconductor, and thus, various colors of light can be used for various purposes. Recently, an illumination device using a high-brightness light-emitting chip has been replacing typical fluorescent lamps or incandescent lamps.
For example, an LED bulb includes a sow block, a heat dissipation structure, a driving circuit, a printed circuit board (PCB), an LED, and a cover. The cover may be generally formed of a semicircle-shaped glass or a plastic material, such as acryl or polycarbonate. Also, to prevent direct exposure of the LED located inside the bulb, a white diffusion coating may be formed on an inner surface of the glass cover when the glass cover is used, and a diffusion material may be mixed with a cover material to embody a light diffusion effect when the plastic cover is used.
However, illumination lamps using a semiconductor light-emitting device have light distribution characteristics which are very different from those of typical incandescent bulbs, because such illumination lamps emits light that progresses only toward a forward direction, not in a direction covering all 360 angle degrees. For example, an LED bulb emits the highest intensity of light at an angle of 0°, and as the angle increases, the intensity of light is reduced. For example, at an angle of about ±90°, the intensity of light is almost 0. On the other hand, a typical incandescent bulb emits a constant intensity of light in an angle range from 0° to about ±130° without a decrease in the light intensity. Accordingly, a full width at half maximum (FWHM) of an irradiation angle of an LED bulb is about 130°, and an FWHM of an irradiation angle of a typical incandescent bulb is about 260°, which is substantially different from that of the LED bulb. This difference is due to the fact that while a filament used in a typical incandescent bulb emits light in a direction covering all 360 angle degrees, an LED irradiates light at an angle of about 120°. Thus, when an LED bulb is used in existing illumination devices, a user may recognize very different light distribution and illumination characteristics from those that the user is accustomed to. This may function as an obstacle to the supply and popularity of the LED bulb.